1. Field of the Invention
The present invention relates to the field of a control technology of transmission power in a radio-communications apparatus (a radio transmitter), such as a mobile terminal device.
2. Description of the Related Art
In a radio-communications apparatus, such as a mobile terminal device, transmission power required for transmitting a radio signal varies depending on factors, such as the dispersion and the temperature characteristics of built-in components which constitute a radio-communications circuit (a radio transmitter) For this reason, in such radio-communications circuit, an APC (Automatic Power Control) circuit is generally employed.
FIG. 10 is a block diagram showing a circuit configuration of a conventional radio transmitter having the APC function.
In FIG. 10, I and Q signals denote the orthogonal signals to be transmitted. An orthogonal modulator 101 carries out an orthogonal modulation processing to the inputted signals, I and Q, and thereafter supplies them to a driver amplifier 102. The driver amplifier 102 amplifies the output signals from the orthogonal modulator 101 according to a gain setting value designated from a base-band circuit 107. The amplified output signals of the driver amplifier 102 are, after being band-limited in a band-pass filter 103, inputted to a power amplifier 104. The signals amplified in the power amplifier 104 are transmitted as radio signals from an antenna 112 through a coupler 110, an isolator 105, and a band-pass filter 113.
In addition, the isolator 105 suppresses the generating of the characteristic degradation of the power amplifier 104 due to the fact that a part of the output signals of the power amplifier 104 is reflected at the antenna 112.
The coupler 110 splits the output signal of the power amplifier 104 into a signal for the APC, and a signal for a transmission wave generation. The signal for the APC is inputted to a detection circuit 111. The detection circuit 111 converts the inputted signal for the APC to a voltage value by detecting and smoothing by a detector (not shown) which uses a diode and the like. The detected result (the voltage value) in the detection circuit 111 is transferred to a CPU (Central Processing Unit) 108 through the base-band circuit 107.
In a memory 109, a transmission power versus detection table (an APC table, not shown) for carrying out the APC has been stored in advance. Then, the CPU 108 carries out a comparison processing by referring to this APC table based on the informed detection result. In this comparison processing, the CPU 108 compares transmission power (target transmission power) which this device itself originally needs with the present transmission power which the detected result indicates.
Then, the CPU 108, as a result of this comparison processing, if the present transmission power is smaller than the target transmission power, instructs the driver amplifier 102 through the base-band circuit 107 to increase the gain. On the other hand, if the present transmission power is larger than the target transmission power, the CPU 108 instructs the driver amplifier 102 through the base-band circuit 107 to lower the gain.
In the conventional radio transmitter having the APC function, the transmission power is maintained to preset target transmission power by the above-described configuration.
However, in the conventional radio transmitter (FIG. 10) described above, in order to detect the present transmission power, the coupler 110 is provided in the transmission signal line. The coupler 110 has a circuit configuration which splits the output signal of the power amplifier 104 into the signal for the APC and the signal for the transmission wave generation, as described above. For this reason, with the circuit configuration shown in FIG. 10, because this coupler 110 is inserted in the transmission signal line, a loss will be generated. Namely, in the conventional radio transmitter shown in FIG. 10, there is a drawback of inviting a degradation of RF (Radio Frequency) characteristic due to the fact that the coupler 110 is inserted in the transmission signal line.
Incidentally, in Japanese Patent Application Laid-Open No. H11-55131 (Patent Document 1) and Japanese Patent Application Laid-Open No. 2002-176368 (Patent Document 2), the APC function mounted in a mobile terminal device of a mobile communications system is disclosed.
In these Patent Documents 1 and 2, the mobile terminal device, when the present transmission power of the mobile terminal device is detected in order to realize the APC function, detects an electric-current of the power amplifier. Then, in these Documents, bias control of the power amplifier itself is carried out according to the result of the electric-current detection. For this reason, in the circuit configuration according to the Patent Documents 1 and 2, a terminal (a bias control terminal), which sets a control signal for realizing this bias control to the power amplifier, is required (refer to a variable gain IF amplifier 11 shown in FIG. 1 in the Patent Documents 1 and 2).
Incidentally, in the conventional circuit configuration shown in FIG. 10 described above, in order to detect the present transmission power to realize the APC function, the coupler 110 is inserted in the transmission signal line. The generation of the loss, which is a problem in the conventional circuit configuration (FIG. 10), is due to the coupler 110.
Then, in place of the coupler 110 in the conventional circuit configuration shown in FIG. 10 described above, a case of employing an APC method disclosed in the above-described Patent Documents 1 and 2 is considered. In this case, the power amplifier (the variable gain IF amplifier 11) disclosed in the above-described Patent Documents 1 and 2 corresponds to the power amplifier 104 shown in FIG. 10.
However, in the conventional circuit configuration shown in FIG. 10 described above, a control signal to be set to the driver amplifier 102 from the base-band circuit 107 is not only for realizing the APC function. Namely, such control signal is set to the driver amplifier 102 so as to realize an AGC (Auto Gain Control) function, in addition to realize the APC function. This AGC function is a function for controlling the gain of the device itself optimally depending on the electric-field intensity at the time of radio communications to a base station. For this reason, even when the APC method disclosed in the above-described Patent Documents 1 and 2 is employed, in order to leave such AGC function, a line which supplies the AGC control signal from the base-band circuit 107 to the input terminal (a control terminal) of the driver amplifier 102 is needed. In other words, this means, when the APC method which uses the power amplifier is employed instead of using the coupler 110, a new line which supplies the control signal for the APC from the base-band circuit 107 to the power amplifier 104 is needed.
Accordingly, when the APC method described in the above-described Patent Documents 1 and 2 is applied to the circuit configuration of the conventional radio transmitter shown in FIG. 10, it is necessary to newly add a bias control terminal described above to the power amplifier 104 so as to supply the control signal for the APC to the power amplifier 104. This will invite a design modification in the circuit configuration of the conventional radio transmitter shown in FIG. 10, therefore, is not a good idea in terms of cost.